Thrombopoietin (TPO), also referred to as c-Mpl ligand, mpl ligand, megapoietin, and megakaryocyte growth and development factor, is a glycoprotein that has been shown to be involved in production of platelets. See e.g., Wendling, F., et. al., Biotherapy 10(4):269-77 (1998); Kuter D. J. et al., The Oncologist, 1:98-106 (1996); and Metcalf, Nature 369: 519-520 (1994). TPO has been cloned and its amino acid sequence and the cDNA sequence encoding it have been described. See e.g., U.S. Pat. No. 5,766,581; Kuter, D. J. et al., Proc. Natl. Acad. Sci., 91:11104-11108 (1994); de Sauvage F. V., et al., Nature, 369: 533-538 (1994); Lok, S. et al., Nature 369:565-568 (1994); and Wending, F. et al., Nature, 369: 571-574 (1994).
In certain instances, TPO activity results from binding of TPO to the TPO receptor (also called MPL). The TPO receptor has been cloned and its amino acid sequence has been described. See e.g., Vigon et al., Proc. Natl. Acad. Sci., 89:5640-5644 (1992).
In certain instances, TPO modulators may be useful in treating a variety of hematopoietic conditions, including, but not limited to, thrombocytopenia. See e.g., Baser et al. Blood 89:3118-3128 (1997); Fanucchi et al. New Engl. J. Med. 336:404-409 (1997). For example, patients undergoing certain chemotherapies, including but not limited to chemotherapy and/or radiation therapy for the treatment of cancer, may have reduced platelet levels. In certain instances, treating such patients with a selective TPO modulator increases platelet levels. In certain instances, selective TPO modulators stimulate production of glial cells, which may result in repair of damaged nerve cells.
Certain TPO mimics have been described previously. See e.g., WO 03/103686A1; and WO 01/21180.